SMOKESTACKS, cooling towers, reactor domes and gas installations are defining features of our modern landscape. Each is a key component in electricity generation, but perhaps not for much longer.

Sprinkled over every continent are the totems of a new era of power: wind turbines and solar energy collectors. So far they are few and far between, but that's about to change. Plans for huge solar power plants have been drawn up in the US, Spain and Portugal, and it seems barely a month goes by without a new wind farm springing up.

In the past decade, the amount of electricity generated from renewables worldwide almost doubled, according to the International Energy Agency, and by 2006 they accounted for 2.3 per cent of the 19 million gigawatt-hours of electrical energy the world produced.

This is set to rise even further in the next few years. In January, the European Union set targets for its member states that would require 20 per cent of its electricity to come from renewable sources by 2020. China plans to reach 15 per cent by the same year. Some US states have introduced similar targets.

On paper, the amount of recoverable renewable energy available globally could serve our needs several times over (see "Earth, wind and fire"). So could we meet all of our energy needs from renewable sources?

It's a tricky question. One problem is that the more energy provided by renewables, the more unstable national electricity grids become. Unlike nuclear, coal or gas-fired power plants, renewable generators only produce electricity intermittently: when the wind is blowing or the sun is shining. So as things stand we will either have to accept more frequent outages, or have to rely on back-up from fossil-fuel or nuclear generators.

With up to 20 per cent from renewables, the problem is manageable - operators already keep back-up plants running to smooth out such fluctuations. It is easily affordable too. Meeting this target with wind alone would add just 50 cents per month to the average US household bill, states a report from the Department of Energy, published in May.

Going beyond this brings more challenges. "At around 30 per cent penetration of renewables it will start causing problems for the utility grids," says Georgianne Peek, an energy researcher at Sandia National Laboratories in Albuquerque, New Mexico. And the further you go, the worse it gets. "We are used to being able to flick the switch and having the lights come on," Peek says. "That won't happen with 100 per cent renewables."

So to make a high level of renewables workable, you need to do more than just install wind turbines and solar panels. Something will also have to be done by the consumer. We are already seeing hints of how this will work in fridges and aircon units that switch themselves off when the electricity supply is overstretched. Similarly, smart metering can dynamically change the price of electricity to encourage people to use power-hungry devices at times when demand is low (see Will the lights stay on?).

Renewable sources can also generate excess power when demand is low. Finding efficient ways to smooth out the peaks and troughs is a top priority (see Saving up for a windless day). Finally, high-voltage direct-current "supergrids" linking areas with significant renewable resources across thousands of miles could shift power more efficiently to regions that need it (see Edison's revenge).

Put all these together, and there is no technical reason that we could not get close to 100 per cent of our electricity from renewables, says Samir Succar, at the Princeton Environmental Institute at Princeton University, who studies energy storage and transmission systems. "I don't see intermittency as an insurmountable obstacle."

Some communities have already managed to make the switch (see From dream to reality). Isn't it time the rest of us followed suit?

Energy and Fuels - Learn more about the looming energy crisis in our comprehensive special report.

From issue 2677 of New Scientist magazine, 08 October 2008, page 28-29

What's a watt worth?

A watt is a measure of power - the rate of flow of energy. A typical TV set has a power consumption of 150 watts, so for an hour's viewing it will consume 150 watt-hours of energy. A large, 10-megawatt wind turbine should produce at least 10,000 megawatt-hours of energy in a year, enough to meet the needs of 1000 average American homes.